It is well known to treat a carbonate ground formation with acid in order to stimulate the well. According to prior art, relatively large quantities of hydrochloric acid have to be pumped into the well. Often the treatment has limited success. If the acid is not flowing into the intended sections of the well, the treatment may even lead to undesired increase in gas and water production.
The lack of desirable effects could be due to a breakdown of the formation matrix or that the acid follows natural fractures in the formation.
Several methods have been proposed for the purpose of improving well productivity. It is thus known to position a deflecting shoe at a lateral opening in the motherbore tubular. A jetting hose attached to coiled tubing is then fed from the surface and deflected through the opening in the motherbore tubular and further on into the formation as the acid dissolves the formation. Although safeguarding that the acid is flowing into the desired part of the formation, the method is producing unnecessary large passages in the formation and the lateral openings are jetted sequentially.
EP 2098679 shows a motherbore tubular having narrow pipes directed towards the ground formation. The narrow pipes are telescopically penetrating the ground formation.
WO 2012105850 proposes to direct a narrow pipe towards the formation. Several narrow pipes that are made to extend into the ground formation may be positioned on or in the motherbore tubular. The narrow pipes may have sensors attached. The document presents a drill bit at the leading end of the narrow pipe. However, apart from a an engine placed close to the drill bit, no method of transferring power to the drill bit is given.